1. Field of the Invention
The present invention relates to information storage and display systems utilizing disk drives, and more particularly, to video recording systems that transfer both time-critical, error-tolerant streaming video data segments and non-time-critical, error-intolerant data segments.
2. Description of the Related Art
Hard disk drives complying with a standard known as ATA (Advanced Technology Attachment) are commonly used in non-audiovisual, computer-related applications which require a high level of accuracy for the data segments transferred between the disk drive and other system components. These non-audiovisual data segments are typically referred to as “information technology” or “IT” data segments. When a host processor sends an ATA data transfer command to the disk drive to transfer an IT data segment, the host processor requires a high level of accuracy for the IT data segment, i.e., that the IT data segment be substantially free of errors. To ensure the required level of accuracy for IT data segments written to the disk drive or transmitted to the other system components, ATA read and write data transfer commands to the disk drive typically require some disk-drive-resident error recovery, in which the disk drive undertakes various error recovery procedures in an attempt to transfer the IT data segment with no data transfer errors. These disk-drive-resident error recovery procedures can include detection, identification, and correction procedures.
For example, these disk-drive-resident error recovery may include multiple retries, or other ‘heroic’ efforts to ensure that the requested IT data segments have the required level of accuracy. Depending on the success of the various retries or other efforts, the disk-drive-resident error recovery may require additional time by the disk drive, thereby possibly delaying the transfer of other data segments. Despite these possible delays, it is generally acceptable in non-audiovisual applications to carry out the disk-drive-resident error recovery to ensure the accuracy of the IT data segments being written or transmitted. Therefore, the IT data segments can be described as non-time-critical, error-intolerant data segments because their transfers may be delayed without sacrificing system performance, but their transfers must not create errors which would lower the level of accuracy of the data segments.
Audiovisual applications for audiovisual or “AV” data segments corresponding to a video data stream have different requirements than do non-audiovisual applications. Audiovisual applications place more importance on the predictability of AV data transfer, while tolerating some loss in AV data accuracy. By their nature, AV data segments must be continually transferred at a required data transfer rate. The required data transfer rate for a video data stream is typically less than the maximum possible data transfer rate for the disk drive, resulting in additional bandwidth available for the concurrent transfer of additional data segments, some of which correspond to other video data streams. Even a small delay in the transfer of an AV data segment can deleteriously affect the system performance and can be quite noticeable to the user. However, because each AV data segment is quickly replaced by the next AV data segment, an error in a particular AV data segment would be nearly undetectable by the user. Thus, AV data segments can be described as time-critical, error-tolerant data segments because their transfers must not be delayed, but their transfers may create errors which would lower the level of accuracy of the data segments.
Audiovisual applications are therefore enhanced by modifications to the standard ATA data transfer command set for hard disk drive usage. One of these modifications has been the introduction of data transfer command sets optimized for audiovisual applications. For example, a document identified as “T13/D99128 revision 0” entitled “Proposal for Audio/Visual Feature Set” available from Western Digital Corporation of Irvine, Calif., and a document identified as “T13D99123 revision 1” entitled “Proposal for Streaming AV Commands” available from Seagate Technology of Longmont, Colo., both of which are incorporated by reference herein, propose alternative data transfer command sets for the storage on hard disk drives of streaming AV data and non-streaming IT data. These data transfer command sets add new instructions to the standard ATA data transfer command set to guarantee the timely transfer of AV data segments at the possible expense of the accuracy of the AV data segments.
As described in the above-referenced “Proposal for Audio/Visual Feature Set” from Western Digital Corporation, the “Streamweaver” data transfer command set incorporates additional data transfer commands into the standard ATA data transfer command set. These additional data transfer commands enable the host processor to alter the disk drive parameters and functions related to AV data transfer by toggling the disk drive between an AV mode and an IT mode. In the AV mode, the disk drive may reconfigure resources to support the streaming requirement of the AV data segments, and may set an upper limit on the total time devoted to error recovery in the event of a data transfer error, thereby constraining any disk-drive-resident error recovery. Similarly, in the IT mode, the disk drive may reconfigure resources to support the accuracy requirement of the IT data segments. In addition, the “Streamweaver” data transfer command set includes a “Read AV Stream” command and a “Write AV Stream” command which require fewer disk-drive-resident error recovery procedures in the event of a data transfer error than are required by the corresponding read and write commands of the standard ATA data transfer command set. Having fewer disk-drive-resident error recovery procedures is an effort to minimize the possibility of delaying the transfer of other AV data segments.
When being used in a video recording system, such as a digital video recorder, a disk drive is typically required to transfer streaming AV data segments concurrently with IT data segments corresponding to information such as an electronic program guide. In such a system, it is desirable that the disk drive transfer the IT data segments with the required high accuracy in response to data transfer commands by the host processor, while maintaining the required data transfer rate for the streaming AV data segments. Because the required data transfer rate for a video data stream is typically less than the maximum possible data transfer rate, there is usually sufficient bandwidth remaining to transfer both the streaming AV data segments and the IT data segments. However, due to the disk-drive-resident error recovery inherent in the standard read and write commands of the ATA data transfer command set, use of the standard read and write commands of the ATA command set for transferring the IT data segments may potentially exceed the available time, thereby interrupting or delaying the streaming AV data segments.